Potted plants often become "root bound" due to incorrect pot size, or simply due to growth of the plant and the confining nature of the pot walls. To eliminate this problem, larger pots are used, or the plant contained within the pot is transplanted into the ground. The difficulty found in transplanting is that spiral growth of roots may continue in the ground, at least temporarily, thereby reducing potential plant performance, especially in short growing seasons.
It has been found that roots take up nutrients only in the first 2 millimeters of the root tips, so it is important that a root system sprout as many small roots as possible. One avenue for obtaining a maximum number of root tips is accomplished by pruning the roots. Of course this procedure is not readily available to a plant growing naturally in the ground.
Mechanical pruning has been accomplished to a limited degree within specially designed planters. U.S. Pat. Nos. 4,442,628; 4,497,132; and 4,716,680 all issued to Whitcomb disclose growth containers which, in some way, are provided to prune roots, either mechanically or by "air pruning." The '680 patent is a mechanical root pruning device with no provision for aeration.
"Air pruning" is a method by which roots may be "pruned" by exposing portions of the root stems to ambient air. Roots exposed to open air abruptly stop growing. Retarded growth in the area influences new root growth in other areas, thereby producing an effect similar to mechanical pruning. Hundreds of secondary or auxiliary roots sprout in place of the "air pruned" root ends. These secondary roots take up nutrients and promote better plant life.
It is advantageous to provide both mechanical and air root pruning while avoiding spiral root growth to maximize the growth and productivity of plants.
German Patent 2,744,143 shows a plant receptacle having a wall configuration with a number of circular apertures formed in the side for permitting outward expansion of roots. The receptacle wall appears to be continuous. The apertures are circular and spaced apart from one another to leave a substantial surface area of the receptacle walls in contact with the planting medium. The circular areas occupied by the apertures and the wall thickness appear to limit air and mechanical pruning by the structure. Furthermore, the circular nature of the apertures, even the flared apertures shown in FIG. 3b of the reference, would not encourage significant soil warming due to reflected sunlight on the aperture surfaces.
French Patent 2,238,422; German Patent 60,174; and German Patent 30,112 all disclose forms of plant arbors utilized to receive growing, above-ground foliage of a plant to hold fruit, blossoms, etc. above the ground surface to avoid spoilage. Of these, German Patent 60,174 discloses a thin apertured wall structure that is selectively based about the fruit plant stocks and is held by a tie wire or string. The apertures in this arrangement are utilized to allow light and air to the stalk and foliage growing therein.
U.S. Pat. No. 4,850,136 to Vollers shows a container with removable wall sections shaped in a rectangular configuration. The primary function of this container is to facilitate separation of the container walls from the root mass to facilitate transplanting.
The above-described apparatus achieve limited purposes in avoiding spiral root growth in some instances and facilitate plant growth or support in others. However, none specifically addresses both issues of air and mechanical root pruning and none facilitates planting within the vertical wall of the planter itself, thereby significantly expanding the planting surface of the planter.